Electric circuit



y 17, 1951 A. J. BROUWER 2,561,048

ELECTRIC CIRCUIT Filed April 12, 1950 I g z carrier figure: gala-afarw-i I INVERTOR Albert Jan Bram/war Ac ENT Patented July 17, 1951ELECTRIC CIRCUIT Albert Jan Brouwer, Hilversum,

signor to Hartford National Netherlands, as- Bank and Trust Company,Hartford, Conn., as trustee Application April 12, 1950, Serial No.155,454

In the Netherlands May 2, 1949 4 Claims. (Cl. 323-75) This inventionrelates to circuits for deriving a voltage adjustable in value andpolarity from a source of voltage, and more particularly to suchcircuits in which the mean momentary potential of the terminals betweenwhich the adjustable voltage is established is equal to the meanmomentary potential at the terminals of the source of voltage.

Circuits of this kind are utilised for feeding a symmetrical loaddevice, for example for supplying adjustable direct voltages to one pairof deflecting electrodes of a cathode ray tube. In order to permitadjustment of the position of the image spot, the direct voltage betweenthe electrodes is required to be adjustable, while in view of distortionthe mean potential of the two electrodes must remain independent of thisadjustment.

In a known circuit of this kind the source of voltage is connected tothe series-combination of a fixed resistance, an adjustable resistanceand a second fixed resistance of the same value. The adjustable voltageis taken off between the two ends of the adjustable resistance. Thisgives rise to the disadvantage that in the case of constant polarity andvalue of the voltage of the source of supply, the adjustable voltage canbe'controlled from a maximum value to the value zero so that thepolarity can never be inverted. This inversion may be achieved, however,by connecting the source of voltage in a suitable manner to twoidentical potentiometers which are coupled mechanically. On account ofthe requirement of symmetry, the potentiometers must, however, possesssubstantially identical characteristic curves, which can be realisedonly with difiiculty and is in any case comparatively expensive.

The invention provides a novel circuit by which the aforesaiddisadvantage is overcome.

In a preferred embodiment of the invention, a source of voltage suppliesa Wheatstone bridge circuit in which, starting from a diagonal connectedto the source of supply, one branch of the bridge includes theseries-combination of ohmic resistances R1, Ra, Re and the other branchof the bridge includes the series-combination of ohmic resistances R3,R2, R1, while the junction of R2 and R3 in one branch of the bridge isconnected to that in the other branch by way of an adjustable resistanceR4, the adjustable voltage being taken ofi between the junction of R1and R: in the two bridge branches and the resistance being soproportioned that the resistance value 2 lies within the region in whichR4 is adjustable. Other embodiments of the circuit 'according to theinvention may be obtained by substituting for all the ohmic resistancesimpedances having the same phase angle and whose values satisfy the samerelations as the ohmic resistances.

By this proportioning the polarity of the adjustable voltage in thiscircuitis found to be inversible by variation of R4 or of thecorresponding impedance with constant polarity of the voltage of thesource of voltage, so that the control range of the adjustable voltageextends from a predetermined positive value to a predetermined negativevalue.

The invention will now 'be explained more fully by reference to theaccompanying drawing wherein:

Fig. 1 is a schematic diagram of one preferred embodiment of theinvention, and

Fig. 2 is a schematic diagram of a second preferred embodiment.

In Figure 1, reference numeral l indicates the source of voltage towhich a bridge circuit is connected. The ohmic resistances R1, R2, R3are included in succession in series in the branch 2-3-4 of the bridgeand the resistances Rs, R2, R1 are included in succession in series in"the branch 2-5-4 of the bridge. An adjustable resistance R4 is providedbetween the points 3 and 5. The adjustable voltage is taken from points6 and 1 and supplied to terminals '8 and 9. The circuit exhibitssymmetry, since point I is connected to the points 2 and 4 in a similarmanner as point 8 is connected to the points 4 and 2. The mean potentialof the points 6 and l is thus equal to that of the points 2 and 4. Thevoltage between 6 and 1 is adjustable by variation of the resistance R4.This voltage is found to be equal to in which e represents the voltagebetween the points 2 and 4. With that resistance value R40 of R4 atwhich the adjustable voltage, it must be ensured that voltage at the twoboundaries of the control range are equal. It R4 min and R4 ma:represent the minimum and maximum values of R4. this is achieved it 4max a'- 1+ Rs) +2R,R; 4 sin a-t 1+ e) i+ a) a 4Inin( I' l+ s) +2RIRI 4min s-t- RI+YRS) l+ 2) RI -In one embodiment it was found that R4 was inthis case an adjustable resistance having a logarithmic characteristiccurve.

The symmetry of the circuit is only dependent upon the fixedresistances, while the characteristic curve of the adjustable resistanceneed not therefor satisfy predetermined requirements.

It is evident that R4 may be replaced by any bipole which is active asan ohmic resistance and by which this resistance may be acted upon insome manner or other.

It, as is shown in Fig. 2, the source of voltage I is in the form of acarrier-wave generator and if R4 is controlled in the rhythm or a signalfrom a source ID in such manner that R4 is exactly equal to R40 in theabsence of the signal, a modulated voltage is set up at the terminals 8and 9 in which the carrier. wave is suppressed. The same result may beachieved with another circuit according to the invention which may be Iderived from the circuit above described by substituting all the ohmicresistances by impedances having the same phase angle. In the Equations1 and 2 the resistance values R1, R2, R3. and R4 are required to bereplaced by the values Z1, Z:

Z1, Z4 of the corresponding impedances. Control of R4 (Z4) in accordancewith the signal I may be eflected by conventional means such as areactance tube.

What I claim is:

l. A- circuit for deriving from a voltage source a voltage adjustable invalue and polarity, the mean momentary potential at the terminalsbetween which the adjustable voltage appears being invariably equal tothe mean momentary potential at the terminals or the source, said cir- 4cult comprising a Wheatstone bridge having first and second branchesconnected in parallel to the terminals of the voltage source, the firstbranch being constituted by three serially connected impedances whosesuccessive values starting from one end of the first branch isrepresented by Z1, Z2 and Z3, the second branch being constituted bythree serially connected impedances whose successive value starting fromthe corresponding end or the second branch is represented by Z3, Z1 andZ1, a control impedance represented by Z4 adjustable within apredetermined range and connected between the junction of impedances Zzvand Z: in the first branch and the junction of impedances Z1. and Z: inthe second branch, and a pair of output terminals connected between thejunction 01 impedances Zr and Z: in the first branch and the junction orZs and Z1 in the second branch, the impedances having relative values atwhich the resultant impedance H Z4 min( i l+ l) 4 min( 2+ l+ I) i+ a) issubstantially satisfied.

3. A circuit as claimed in claim 1, characterised in that the impedancesare constituted by ohmic resistances.

4. A circuit, as set forth in claim 1, wherein said voltage source isconstituted by a carrier wave generator and wherein said controlimpedance Z4 is varied throughout its range in ac- I cordance with amodulation signal, whereby a suppressed carrier modulated wave isdeveloped at said output terminals. j

' ALBERT JAN BROUWER No references cited.

